1. Field of the Invention
The present invention relates to an optical material, an optical device fabricated therefrom, and a method for fabricating the same, and more particularly to an optical material, an optical device fabricated therefrom, and a method for fabricating the same utilizing a metamaterial
2. Description of the Related Art
It is known that when a light wave inputs into a boundary surface between materials having different refractive indices from one another, reflection of the light appears in the boundary surface as an optical phenomenon.
There are a variety of manners for interpretation as to the optical phenomenon. One of these interpretations is in that since a difference in refractive indices between materials functions as a potential barrier for a light wave, a part of the light wave is reflected. Another interpretation is in that when there is impedance mismatching in an electric circuit, electric signals are reflected at that point, and such impedance mismatching is equivalent to a difference in refractive indices for light likewise.
In general, reflection of light appearing in a boundary surface due to inputting a light wave into the boundary surface between materials having different refractive indices can be eliminated with respect to a light having a specified polarization, when a particular surface treatment such as dielectric multilayer coating is applied. Accordingly, it is possible that a reflection coefficient is allowed to be zero by means of a particular surface treatment such as the above-described dielectric multilayer coating. In this respect, it is known also that such reflection of light can be made to be zero under a particular condition.
The particular condition means that for inducing a phenomenon wherein reflection of light becomes zero known by the name of “Brewster” in optics (hereinafter referred to as “Brewster phenomenon” in the present specification). The conditions for inducing such Brewster are called “Brewster conditions” wherein both the following two conditions (a) and (b) must be satisfied.
More specifically, the two conditions (a) and (b) are:
(a) A light wave inputs into a boundary surface between materials in the form of p-polarization; and
(b) The light wave inputs into the boundary surface at a particular incident angle determined by refractive indices of two materials forming the boundary surface (the incident angle is called “Brewster's angle”).
Thus, the above-described two conditions (a) and (b) must be satisfied for inducing the Brewster phenomenon, but there is a restriction of the above-described condition (a), so that it is possible to make a reflection coefficient to be zero at the boundary surface due to the Brewster phenomenon in only the case where a light wave is in p-polarization. Accordingly, there is such a problem that such Brewster phenomenon cannot be induced with respect to a light wave in s-polarization, so that reflection cannot be eliminated in the boundary surface except that either a particular surface treatment such as dielectric multilayer coating is applied, or a refractive index difference of a material is made to be zero.
On the other hand, there is a strong demand for eliminating a reflection loss appeared on surfaces of a lens, a mirror, and a window application in, for example, a laser resonator or an optics system of optical communication systems as much as possible. Particularly, there is a case where significant decrease arises in characteristic properties due to a slight reflection loss inside a resonator of a laser and the like, so that it is requested that the reflection loss is allowed to be close to zero as much as possible.
For this reason, such a manner that an end surface of an optical device is cut off into a Brewster's angle in a laser resonator or an optics system of optical communication systems, whereby the above-described condition (b) is satisfied to decrease the reflection loss is frequently applied.
As mentioned above, however, since a Brewster phenomenon is that appearing only concerning a light in p-polarization, zero reflection loss is obtained only with respect to a light wave of a p-polarization component as a result of satisfying the above-described condition (b). Such a problem that a reflection loss yet appears as to an s-polarization component still remains.
Hence, a difference appears between both application efficiencies in the p-polarization component and the s-polarization component in the laser resonator or the optics system of optical communication systems wherein an end surface of the optical device is cut out in a Brewster's angle. For instance, at the mention of a laser resonator, an oscillation light of the laser resonator wherein the end surface of an optical device has been cut out in a Brewster's angle becomes a linearly-polarized laser beam having finally a p-polarization component only. Furthermore, when an optical device the end surface of which has been cut out in the Brewster's angle is used in an optical communication system, the optics system having extremely high polarization dependency is obtained. Efficiency of such optics system decreases extremely, when a polarization direction of the incident light differs from a polarization plane direction of the optics system at the time of design thereof.
As described above, a Brewster phenomenon has strong polarization dependency; and in this respect, the polarization direction of a light wave still remains remarkable dependency with respect to the structure of a dielectric multilayer film by which the reflection coefficient may be made to be zero. Thus, it is impossible to realize such a coating by which the reflection coefficient may be made to be zero independent of the polarization direction.
As described above, reflection of a light wave arises inevitably in the boundary surface between two materials having different refractive indices from one another. In this connection, a manner for making the reflection to be zero is to utilize the Brewster phenomenon.
In the prior art, however, even when the Brewster phenomenon is used, such Brewster phenomenon cannot be induced in only p-polarization. As a result, there is such a problem that an optical device utilizing the Brewster phenomenon or a system involving the optical device comes to have strong polarization dependency. For this reason, it is strongly demanded to develop such optical material or optical device independent of a polarization direction, whereby the reflection coefficient may be made to be zero.